This invention relates to a burner, and more particularly to a burner for high temperature combustion wherein the interior burner wall is protected from the heat of combustion by a primarily gaseous shield, and wherein the gaseous shield is substantially made up of water vapor or carbon dioxide or a combination of water vapor and carbon dioxide.
High temperature combustion reactions are useful, because they encourage the conversion of carbon monoxide to carbon dioxide, the combustion of relatively large organic molecules, and the combustion of xe2x80x9csoot.xe2x80x9d The high temperature combustion reaction results in less production of pollutants than a lower temperature combustion, given the same source of fuel.
The use of burners to produce or contain high temperature combustion reactions is well known, and a variety of methods have been adopted to permit high combustion temperatures. As the temperature of the combustion reaction is increased, such as occurs when the oxidizing agent is enhanced air (air having more than the naturally occurring fraction of oxygen) or near pure oxygen, it becomes necessary to either fabricate the burner from heat resistant materials such as refractory, (or so-called refractory metals) or to provide for a means to cool the burner walls, i.e. remove the heat energy that is delivered to the burner walls by the combustion reaction.
Refractory materials, whether ceramic or metallic, tend to be more costly from both raw material and fabrication aspects, than commonly fabricated materials such as low alloy steels.
While a cooling jacket provides means for cooling the walls of a burner, the construction of a cooling jacket adds a fabrication cost that may be desirable, but is not necessary to the practice of the present invention.
U.S. Pat. No. 4,416,613 to Barisoff discloses a blowpipe (tubular) burner where the flame is contained in the tubular burner, and the burner incorporates a jacket carrying air as a cooling medium. Ambient air passes through the jacket in a counterflow direction, and all of the cooling air is discharged through the combustion process. Some of the cooling air is used in the combustion process, and the balance of the cooling air is xe2x80x9cexpelled through annular end (27) as an annular gaseous shield (32) between the outer wall of the inner tubular shield (25) and the central flame (33).xe2x80x9d Barisoff at Column 3, Line 23.
The annular gaseous shield of the present invention differs from the one taught by U.S. Pat. No. 4,416,613 to Barisoff in important aspects. For example, the invention of Barisoff uses only air as a cooling medium, while the present invention uses a gas that is primarily made up of water vapor or carbon dioxide, as opposed to the incidental amounts of water vapor and carbon dioxide present in ambient air.
U.S. Pat. No. 5,372,857 to Browning discloses a tubular burner where the combustion process proceeds within an internal tube, and where a jacket is provided and the cooling medium in the jacket is described as being steam. The inventor notes that cooling is achieved by the evaporation of water passing over (outside) of the tube that contains the combustion reaction (Column 1, line 39 and Column 3, lines 8-11 and lines 21-23).
U.S. Pat. No. 4,931,013 to Brahmbatt, et al, discloses a burner that has concentric passages for the passage of air, fuel and oxygen. These passages are intended to facilitate the mixing of these three constituents at the end or face of the burner, where a combustion reaction is taking place. The concentric structure is disclosed, and the body of the disclosure describes the cooling effect of passing combustion air through the burner so as to obviate the need for additional burner cooling. This apparatus does not contain the flame or combustion process, rather the cooling is desirable to protect the burner tip itself.
U.S. Pat. No. 5,217,363 to Brais, et al discloses a burner that has concentric passages for the passage of air, fuel and oxygen. It appears to have the same general objectives as the ""013 patent, and has a jacket that is arranged to cool the outside wall of the burner with a flow of air.
U.S. Pat. No. 5,454,712 to Yap discloses a burner where the burner is protected from the highest heat of the flame by the presence of a swirling flow of air that joins the combustion at a distance from the burner.
U.S. Pat. No. 4,642,047 to Gitman discloses a burner having a liquid-filled cooling jacket.
U.S. Pat. No. 4,666,397 to Wenning, et al discloses a burner that has a hollow nozzle that can be cooled by flowing a medium within the hollow nozzle section, outside of the volume occupied by the combustion reaction.
U.S. Pat. No. 4,887,800 to Hotta, et al discloses a nozzle for burning coal, where the nozzle is cooled by a water jacket.
The present invention contemplates a tubular burner unit (typically a hollow cylindrical shape) having means to introduce a fuel and an oxidizer to a central area at one end of the burner, and may be provided with a means of igniting the fuel. A burner unit according to the present invention will also have openings at or near the combustion initiation end of the burner for the introduction of a gaseous medium that will flow in a curtain-like fashion close to the interior wall of the burner. The gaseous medium provided is made up of a substance that has a relatively high heat capacity (i.e. requiring a relatively high amount of energy to raise the temperature of a unit of mass), such as water or carbon dioxide, as opposed to using an air-like mixture for the transfer of some of the heat energy.
The temperature of combustion tends to increase as the oxidizer becomes more concentrated, i.e. as the percentage of oxygen in the oxidizer increases, so does the temperature of combustion. When nearly pure oxygen is used, a very high temperature is produced, in some cases as high as about 5,000 degrees Fahrenheit. The use of high oxygen concentrations is desirable to minimize the production of oxides of nitrogen, but results in a flame that is very bright and radiant.
The present invention relies on an annular stream or curtain, made up primarily of water vapor or carbon dioxide or a mixture of water vapor and carbon dioxide, disposed between the combustion reaction and the inside wall of the burner. The annular stream of cooling medium functions to intercept and absorb some of the heat of combustion before it can be transmitted to the wall of the burner by the radiated, conducted and convection heat energy of the combustion reaction. Water vapor and carbon dioxide are desirable for this function because these compounds are relatively efficient and ready absorbers of the energy radiated by the incandescent light of the high temperature combustion reaction.
It is possible to control or modulate the temperature of the burner wall by varying the mass flow rate and composition of the cooling medium, e.g by changing the ratio of water vapor to carbon dioxide, or by introducing other constituents to the cooling medium stream, or by regulating the incoming temperature of the gaseous cooling medium, or by a combination of these factors.
Because it is possible to maintain the temperature of the burner tube with the annular stream of cooling medium, it becomes unnecessary to provide for cooling of the burner tube from its outside. A burner according to the present invention can have a burner tube that is efficiently insulated (such as with a vacuum jacket or other heat insulating medium), and force the heat of combustion to be carried by the gaseous cooling medium.
It is an object of the present invention to reduce the amount of energy transmitted to the walls of a burner, so that a given burner may be operated at a higher combustion temperature than it could be, without the gaseous curtain.
It is an object of the present invention to provide a low cost apparatus for performing high temperature incineration.
It is a further object of the present invention to enable the combustion of fuels using nearly pure oxygen, in order to minimize the production of oxides of nitrogen.
The present invention relates to a burner for high-temperature combustion that may be adapted and adjusted to optimize the combustion reaction. Specific features of the invention will be apparent from the above and from the following description of the illustrative embodiments when considered with the attached drawings and the appended claims.
In summary, and in accordance with the above discussion, the foregoing objectives are achieved in the following embodiments.
1. A high-temperature burner comprising:
a hollow burner tube having a combustion end, an open discharge end, and an interior wall;
a burner cap located at the combustion end of the hollow burner tube;
a fuel delivery means in the burner cap, having an opening for the discharge of fuel to the interior of the hollow burner tube, where the opening for discharging fuel is located near the longitudinal axis of the hollow burner tube;
an oxidizer delivery means in the burner cap, having an opening for the discharge of oxidizer to the interior of the hollow burner tube, where the opening for discharging the oxidizer is located between the longitudinal axis of the hollow burner tube and the interior wall of the hollow burner tube; and
cooling medium delivery means in the burner cap, having an opening for the discharge of a cooling medium to the interior of the hollow burner tube, where the opening for discharging the cooling medium is located between the opening for discharging the oxidizer and the interior wall of the hollow burner tube.
2. A high temperature burner as described in Paragraph 1 where the hollow burner tube is made of a ceramic material.
3. A high temperature burner as described in Paragraph 1 where the hollow burner tube is made of silicon carbide material.
4. A high temperature burner as described in Paragraph 1 where the opening for discharging the oxidizer is a series of annular-spaced holes and the opening for discharging the cooling medium is a series of annular-spaced holes.
5. A high temperature burner as described in Paragraph 1 where the opening for discharging the oxidizer is an annular shaped hole, and the opening for discharging the cooling medium is an annular shaped hole.
6. A method of burning materials comprising:
(a) providing a burner having
a hollow burner tube having a combustion end, an open discharge end, and an interior wall;
a burner cap located at the combustion end of the hollow burner tube;
a fuel delivery means in the burner cap, having an opening for the discharge of fuel to the interior of the hollow burner tube, where the opening for discharging fuel is located near the longitudinal axis of the hollow burner tube;
an oxidizer delivery means in the burner cap, having an opening for the discharge of oxidizer to the interior of the hollow burner tube, where the opening for discharging the oxidizer is located between the longitudinal axis of the hollow burner tube and the interior wall of the hollow burner tube; and
cooling medium delivery means in the burner cap, having an opening for the discharge of a cooling medium to the interior of the hollow burner tube, where the opening for discharging the cooling medium is located between the opening for discharging the oxidizer and the interior wall of the hollow burner tube;
(b) providing a fuel to the fuel delivery means and an oxidizer to the oxidizer deliver means;
(c) initiating a combustion reaction between the fuel and the oxidizer to produce hot exhaust products; and
(d) providing a gaseous cooling medium to the cooling medium delivery means and inducing a flow of gaseous cooling medium between the combustion reaction and the interior wall of the hollow burner tube.
7. A method of burning materials as described in Paragraph 6, where the gaseous cooling medium is primarily water.
8. A method of burning materials as described in Paragraph 6, where the gaseous cooling medium is primarily a mixture of water and carbon dioxide.
9. A method of burning materials as described in Paragraph 7 further comprising:
(e) directing the hot exhaust products to a heat exchanger; and
(f) transferring some of the heat of the hot exhaust products to the cooling medium.
10. A method of burning materials as described in Paragraph 6, where the oxidizer is enriched air having at least 28 percent oxygen gas.
11. A method of burning materials as described in Paragraph 10, where the gaseous cooling medium is primarily water.
12. A method of burning materials as described in Paragraph 10, where the gaseous cooling medium is primarily a mixture of water and carbon dioxide.
13. A method of burning materials as described in Paragraph 11, further comprising:
(e) directing the hot exhaust products to a heat exchanger; and
(f) transferring some of the heat of the hot exhaust products to the cooling medium.
14. A method of burning materials as described in Paragraph 12, where the gaseous cooling medium is partially made of the hot exhaust products of the combustion reaction.
15. A method of burning materials as described in Paragraph 14, further comprising:
(e) directing the hot exhaust products to a heat exchanger; and
(f) transferring some of the heat of the hot exhaust products to the cooling medium via the heat exchanger.